<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>c3盒子模型</title>
    <style>
        div:nth-child(1) {
            width: 200px;
            height: 200px;
            background-color: deepskyblue;
            padding: 10px;
            border: 2px solid #666;
        }
        div:nth-child(2) {
            box-sizing: border-box;
            width: 200px;
            height: 200px;
            padding: 10px; 
            border: 2px solid #666;
            background-color: dodgerblue;
        }
    </style>
</head>
<body>
    <div></div>
    <div></div>
</body>
</html>